1. Field of the Invention
The present invention relates generally to a spiral antenna. More specifically, the present invention relates to an archimedean spiral antenna which has a reduction in the required size of its antenna diameter and length.
2. Description of the Prior Art
In the past the design of spiral antennas has been limited by two criteria with respect to the spiral antenna's lowest desired frequency of operation. First, the diameter for a sum type mode of operation (simple cosine power pattern) has to be a minimum of one wavelength divided by PI. The length of a typical spiral antenna assembly with an embedded printed circuit balun feed need to be one half wavelength.
For example, a spiral antenna which is required to operate at one Gega-hertz (GHz) without a serious decrease in gain would result in a spiral antenna with a diameter of 3.75 inches and a length of 6.0 inches.
However, for this example, there is a need to reduce the diameter for a spiral antenna from 3.75 inches to about 2.0 inches and perferably about 1.85 inches. Further, for this example, there is also a need to reduce the length of the spiral antenna to about 2.5 inches and provide for a volume reduction by a factor of five.
Previous designs for spiral antenna size reduction have used dielectric loading with limited success. The frequency bandwidth has been limited to approximately 2 to 1, and length reduction has not been addressed.